橡胶微粉对无机聚合物胶凝材料力学性能的影响

主要研究了橡胶微粉对无机聚合物砂浆和水泥砂浆力学性能的影响.实验结果表明,随着橡胶微粉掺量的增加,无机聚合物砂浆和水泥砂浆的抗压强度、抗折强度均有所下降,其中无机聚合物砂浆弹性模量降低、变形能力增强、弯曲韧性系数稍有降低;水泥砂浆弹性模量升高、变形能力下降、弯曲韧性系数下降.分析材料微观破坏形貌后发现,与水泥砂浆相比,橡胶微粉与无机聚合物砂浆界面粘结较好,粘结强度高,从而造成无机聚合物砂浆和水泥砂浆这两种材料体系在橡胶微粉掺杂后力学性能的差异.     

橡胶粒径和掺量对水泥基材料收缩和抗开裂性能的影响

本文考虑了粉末状和颗粒状两种典型粒径的橡胶,定量研究橡胶粒径和掺量对水泥基材料收缩和抗开裂性能影响。采用直接测量长度的方法研究橡胶对水泥基材料自由收缩的影响;采用圆环约束收缩实验方法研究橡胶对水泥基材料约束收缩和抗开裂性能的影响。试验结果表明:橡胶的掺入会加剧水泥基材料的自由收缩。橡胶掺入量相同时,掺入橡胶粉末的水泥基材料比掺入橡胶颗粒的水泥基材料自由收缩率高。橡胶的掺入会抑制水泥基材料的约束收缩和开裂。橡胶掺入量相同时,掺入橡胶粉末的水泥基材料比掺入橡胶颗粒的水泥基材料抗开裂性能好。     

高吸水树脂与减缩剂复合对水泥砂浆自收缩的影响

研究了高吸水树脂(SAP)、减缩剂(SRA)在单独使用以及两者复合使用时对水泥砂浆自收缩的影响。结果表明,单独掺入SAP时,能较大幅度改善水泥砂浆的自收缩,且随着SAP掺量的增加,内养护水引入量的增大,降低水泥砂浆自收缩的作用更显著。单独掺入SRA时也能相应地减少水泥砂浆的自收缩,但减缩的效果不及单掺SAP组。互掺各组的减缩效果均比相对应的单掺组优异,SAP与SRA对减少水泥砂浆的自收缩不仅表现出了较好的相容性,而且产生了良好的"叠加"效果。对于互掺组的减缩效果,在变化SAP或SRA掺量时,增加SAP掺量的"叠加"效果要优于增加SRA掺量。     

加掺合料高性能混凝土早龄期收缩特性

采用新研制的智能型非接触式微位移传感器法对加掺合料高性能混凝土从成型后6h到3d龄期内的自生收缩和单面干燥条件下的总收缩进行试验研究,结果表明:掺入硅灰会略微增加混凝土早期自生收缩,而对早期干燥收缩影响不大;粉煤灰的掺入能大幅度地减小混凝土早期自生收缩,但使早期干燥收缩增加;磨细矿渣只有在掺量较多时才能明显降低早期自生收缩,却对早期干燥收缩不利。     

SHPB劈裂试验下橡胶水泥砂浆的动态力学、能量特性及破坏机理试验研究

基于静载巴西劈裂原理,开展了橡胶水泥砂浆的分离式霍普金森压杆(SHPB)劈裂试验,对其动态力学、能量特性及破坏机理进行了研究.根据损伤力学,从强度和能量的角度分析了橡胶掺量、养护湿度和冲击荷载对水泥砂浆动态劈裂损伤的影响,并探讨了三种损伤因素下的六种损伤路径.结合圆盘试件的破坏模式,建立了冲击劈裂简化平面理想受力模型,分析了破裂方式-Ⅰ和破裂方式-Ⅱ两种截然不同的动态劈裂方式,并初步探讨了破裂方式-Ⅱ下圆盘试样的破坏机理.结果表明,掺入橡胶颗粒和降低养护湿度均降低了水泥砂浆的动态劈裂拉伸强度;普通水泥砂浆和橡胶水泥砂浆有着相同的应力率和应变率演化趋势;掺入橡胶颗粒和降低养护湿度均在一定程度上阻碍了能量在水泥砂浆圆盘试件中的传递;不同的单一损伤因素和复合损伤因素对水泥砂浆圆盘试样造成的动态劈裂损伤不同;在较大的冲击荷载下,圆盘试样会因"三角形压碎区"、"劈裂拉伸区"和"弯曲断裂区"的形成而被破坏.最后,从细观的角度分析讨论了界面过渡区(ITZ)对SHPB劈裂下橡胶水泥砂浆强度和抗冲击性能的影响.     

钢纤维-橡胶/混凝土单轴受压全曲线试验及本构模型

将钢纤维(SF)掺入橡胶混凝土中,能够改善由于橡胶颗粒掺入导致的强度降低,并进一步增加延性。为研究SF-橡胶/混凝土的抗压性能,配制得到SF体积分数分别为0vol%、0.5vol%、1.0vol%和1.5vol%及橡胶颗粒等体积替换砂率为0%、10%和20%的10组SF-橡胶/混凝土试件,并进行单轴受压全曲线试验。结果表明:SF的桥联作用及其与橡胶颗粒的协同作用可改善混凝土的抗压性能,试件破坏呈明显延性特征。随SF掺量的增加,SF-橡胶/混凝土试件的抗压强度及弹性模量均明显增大,其相应峰值应力的应变及全曲线峰值后延性也相应增加;随橡胶颗粒掺量的增加,SF-橡胶/混凝土试件相应峰值应力的应变及全曲线峰值后延性增加,而抗压强度及弹性模量有所减小。在已有研究基础上,通过曲线拟合试验数据,提出适用于SF-橡胶/混凝土的单轴受压应力-应变全曲线数学表达式,模型与试验结果吻合较好,为此类混凝土的结构分析设计提供了理论基础。      

水泥砂浆弹性模量随温度的演化规律

弹性模量作为水泥砂浆重要的性能参数和结构设计参数,对于保障构件的服役安全性和可靠性至关重要。为解决水泥砂浆在低温与高温服役条件下的弹性模量准确测量的技术难题,将修正缺口环法与相对法结合(称为修正缺口环相对法),成功测得了硅酸盐水泥砂浆在-70～800℃下的弹性模量,并研究了饱水与干燥砂浆试样的弹性模量随温度变化的演变规律。测试结果表明:由室温降至-70℃,冰的填充与胶粘作用会使得饱水砂浆的弹性模量增加32. 67%,且模量增长速率随着温度的降低逐渐增大;而干燥砂浆的水分含量较低,其弹性模量在降温过程中基本保持不变。由室温升至800℃过程中,由于水化产物的高温脱水分解与微结构劣化,饱水砂浆的弹性模量降低了93. 78%,而干燥砂浆的弹性模降低了83. 51%,且模量衰减速率随着温度的升高而逐渐降低。     

硅烷复合乳液对水泥砂浆干燥收缩性能及力学性能的影响

将氧化石墨烯/异丁基三乙氧基硅烷复合乳液(GO/lBTS复合乳液)和正硅酸四乙酯/异丁基三乙氧基硅烷复合乳液(TEOS/lBTS复合乳液)分别内掺到水泥砂浆中,研究了两种硅烷复合乳液在不同掺量下对砂浆在养护过程中的干燥收缩性能、水分散失和力学性能的影响.研究结果表明:GO/lBTS复合乳液能有效抑制砂浆的干燥收缩和水分散失,当掺量为2％时,砂浆干燥收缩量和水分散失量达到最小,而且力学强度达到平均最高;TEOS/lBTS复合乳液对砂浆干燥收缩和水分散失的抑制作用不明显,但是当掺量为2％时,力学性能达到最大,抗压强度和抗折强度分别提高了5％和17％;但两种硅烷复合乳液掺量不宜超过水泥质量的3％.通过SEM、EDS测试发现,GO/lBTS复合乳液会在砂浆内部形成一层分散均匀的絮状结构.另外,红外光谱测试结果表明,硅烷复合乳液通过化学键与水泥基材料相结合.     

石墨烯改性水泥基材料的力学和收缩性能

研究了石墨烯对水泥基复合材料的抗压抗折强度、劈裂抗拉强度、流变性能等力学性能的影响,及石墨烯对水泥砂浆自收缩和干燥收缩等变形性能的影响.结果表明:石墨烯会增加水泥浆体的粘度,水泥净浆的流变特性符合宾汉姆流体模型;掺加适量石墨烯能够提升水泥基材料的力学性能,并且对水泥基材料的自收缩及干燥收缩具有显著的抑制效果.力学和收缩...     

碳纳米管增强水泥基复合材料的自收缩及抗裂性能碳纳米管增强水泥基复合材料的自收缩及抗裂性能

水泥基材料的收缩开裂已经成为其破坏的一个主要原因,受到国内外关注,碳纳米管（CNTs）作为一种纳米纤维状材料,可能可以抑制水泥基材料收缩。本文将CNTs放入水中,经过超声处理分散后,形成CNTs分散液,设置不同的CNTs掺量将其掺入到水泥基材料中,通过波纹管实验及圆环试验对该种新型复合材料的自收缩及抗裂性能进行研究。结果表明:CNTs的掺入可以很大程度上抑制水泥基材料的自收缩,最高降低率可到40%以上,且明显提高了水泥基材料的抗裂性能。水灰比的增加会提高CNTs对水泥基材料收缩的抑制效果。当CNTs的掺量为0.1wt%时,可以获得最优效果。同时,CNTs的掺入不仅对水泥基材料自收缩有抑制作用,一定程度上也会抑制水泥基材料的干燥收缩。通过将CNTs掺入到建筑结构关键部分的水泥基材料中,可以提高建筑安全系数。      

Mussel Inspired Modification of Rubber Crumbs for Improved Interfacial Adhesion in Rubber Cement Mortar

Crumb rubbers exhibit extensive potential applications as infrastructure materials due to the low elastic modulus. Nevertheless, the poor interfacial adhesion between rubber crumb and cement matrix limits the scale applications of crumb rubbers in cement-based composites. In this study, mussel-inspired modification of crumb rubbers is investigated. The hydrophilicity of rubber surface has apparently improved after polydopamine (PDA) modification. Effects of the surface modifications of rubbers on the compressive strength, fluidity, and tribology behaviors of rubberized mortars have been systematically characterized. The superiority of PDA modification for crumb rubbers has been demonstrated by comparing those with the other polyphenol modifications and the routine oxidation modification. The compressive strength of the PDA modified rubber cement mortar increases by 37% comparing with that of the ordinary rubber cement mortar. The mechanical and low-temperature tribology behaviors of PDA-rubberized mortars indicate a promising way to improve the service performance of the rubberized mortars and concretes.

     

The use of microfine cement to enhance the efficacy of carbon nanofibers with respect to drying shrinkage crack resistance of portland cement mortars

Significant research has recently been aimed at quantifying the effects of carbon nanofibers and carbon nanotubes in portland cement pastes and mortars. Such efforts have shown that mechanical properties can increase with low concentrations of carbon nanofibers but have marginal improvement or are negatively affected with high concentrations. The objective of this paper is to evaluate the use of a microfine cement to enhance the efficacy of carbon nanofibers in portland cement mortar with respect to cracking resistance via enabling higher nanofiber concentrations. Experiments are performed with concentrations of carbon nanofibers up to 3% by weight of cement using either Type I/II or microfine cement. The primary test implemented was a restrained ring drying shrinkage test; unrestrained drying shrinkage tests, elastic modulus tests, and scanning electron microscopy imaging were performed to provide supplemental data to explain the observations from the restrained ring drying shrinkage tests. It was found that Type I/II cement mortars either lost performance or had insignificant gains with respect to cracking resistance, and all Type I/II mortar mixtures had losses in stiffness with the addition of high concentrations of carbon nanofibers. In contrast, microfine cement mortars had increased shrinkage cracking resistance and no loss in stiffness with increasing amounts of carbon nanofibers (up to the 3% by weight of cement tested in this research). The microfine cement mortar with 3% carbon nanofibers by weight of cement delayed the experimentally measured time of cracking in the ring test by a factor of up to 3.89. The delay in visible cracking time was attributed to microcrack bridging by the carbon nanofibers as imaged by scanning electron microscopy.     

Characteristics of cement-soil mortars

Cement-soil mortars are commonly used for the construction of soil-cement block masonry. The paper focuses on an experimental study in understanding the various characteristics of cement soil mortars in fresh and hardened state. Workability, strength, water retentivity, shrinkage and stress-strain characteristics of cement soil mortars and bond strength of soil-cement block couplets using such mortars are examined. Characteristics of 1:6 cement mortar and 1:1:6 cement lime mortar are also examined for the purposes of comparison. Workability of mortars has been quantified by conducting flow table tests. Results of flow values obtained for mortars from various construction sites are reported. There is a linear relationship between flow and water cement ratio of the mortars. Flow increases with increase in water-cement ratio. Very high flow value of 130% can be achieved for cement soil mortars and cement lime mortars. Reduction in flow value from 100% to 80% leads to increase in strength and modulus of mortars. Clay fraction of the mortar mix controls the flow, strength, density, shrinkage value and modulus of cement soil mortars. Cement-soil mortars lead to better tensile bond strength for soilcement block couplets when compared to the cement mortar and cement lime mortar.     

Understanding the drying shrinkage performance of alkali-activated slag mortars

In this work, drying shrinkage of four alkali-activated slag (AAS) mortars, prepared using various types/dosages of activator, was characterized at four different levels of relative humidity (RH) and two drying regimes (i.e. direct and step-wise drying). The results show that drying shrinkage values of AAS are significantly dependent on the drying rate, as AAS shrinks more when the RH is decreased gradually, instead of directly. At high RH, the drying shrinkage of AAS exhibits a considerable visco-elastic/visco-plastic behavior, in comparison to ordinary portland cement (OPC). It is concluded that the cause of high-magnitude shrinkage in AAS mortar is due to the high visco-elastic/visco-plastic compliance (low creep modulus) of its solid skeleton. Furthermore, the activator affects the shrinkage behaviors of AAS by influencing the pore structure and mechanical properties.     

Effect of aggregates and water contents on the properties of magnesium phospho-silicate cement

Properties of magnesium phospho-silicate cement (MPSC) mortars with different fine aggregates, and different water contents were investigated in the present work. Three types of fine aggregates, natural sand, dead burnt magnesia and alumina particles were used. Two types of hard burnt magnesia powder with MgO content 89.51 and 71.50 wt.% were used as binder. Compressive strength of MPSC mortar with different water/binder ratios were determined at ages of 1, 3, 7, and 24 h. The 3, 7, and 28 day compressive strength and modulus of elasticity were also tested. It was found that the compressive strength of MPSC mortar decreases with the increase of sand content, regardless of sand type. However, the strength reduction of MPSC mortars formed with magnesia and alumina sand was much smaller than that of mortars formed with natural sand. Moreover, in spite of the raw materials, compressive strength and elastic modulus of MPSC decreased with the increase of water/binder ratio at all ages. The hydrate products were analysed by XRD and TG-DTA, and the porosity of MPSC mortar was analysed by MIP. Results showed total porosity increased with the increase of water content. The content of hydrate product of MPSC, phosphate hexahydrate, also increased with the increase of water content. However, it seems that the change of mechanical properties of MPSC is mainly controlled by increase of total porosity which was determined by water content.     

Experimental investigation of drying shrinkage cracking of composite mortars incorporating crushed tile fine aggregate

Drying shrinkage is generally classified as an important hardened concrete property. It expresses the strain occurring in hardened concrete due to the loss of water. During the drying process, free and absorbed water is lost from the concrete. When the drying shrinkage is restrained, cracks can occur, depending on the internal stresses in the concrete. The ingress of deleterious materials through these cracks can cause decrease in the compressive strength and the durability of concrete. In this study, being as a fine aggregate in mortars, crushed tile (CT) effect on drying shrinkage and drying shrinkage cracking is investigated. Thus, compressive and flexural strength, modulus of elasticity, and free and restrained drying shrinkage tests are conducted on mortar specimens produced with and without crushed tile fine aggregate. The ring test has been used in order to investigate the cracks induced by restrained drying shrinkage. In this way, free drying shrinkage strain, along with the number and development of drying shrinkage cracks, of the crushed tile fine aggregate mortar composites are quantified and observed.     

机制砂砂浆干缩性能的研究

研究了砂灰比对石灰岩机制砂砂浆干缩率、不同类型砂对砂浆干缩率、不同石粉含量对砂浆干缩率的影响。结果表明,随着砂灰比的减小,即水泥浆量的增加,干缩率呈增大的趋势;但在水泥浆未填充满砂子空隙之前,随着水泥浆的增加,干缩率的增幅很小,当填充满之后继续增加,增幅明显变大。在早期(≤7d),石灰岩机制砂砂浆的干缩率大于花岗岩和石英岩机制砂,在后期(>7d),花岗岩和石英岩机制砂砂浆的干缩率大于石灰岩机制砂;在各个龄期,3种机制砂砂浆的干缩率均大于河砂的。随着石粉含量的增大,机制砂砂浆的收缩率先减小后增大。在早期(1d、3d),石粉含量为10%时砂浆干缩率最小;在后期(≥7d),石粉含量为15%时砂浆干缩率最小。     

Effects of partial oxidation of crumb rubber on properties of rubberized mortar

It is a generally accepted result that the inclusion of rubber particles causes the concrete to degrade physical properties of the concrete. In this study the crumb rubber was partially oxidized and used as additives of mortars. Dramatically, the compressive strength of the rubberized mortars (with 6 wt.%) was greater than that of mortars without the crumb rubber. To understand these phenomena, Fourier Transform Infrared Spectroscopy (FTIR) was used to explore the functional groups on surfaces of the crumb rubber, and Scanning Electron Microscopy (SEM) was used to observe microstructures of mortars. With the partial oxidation treatment, rubber surfaces produced hydrophilic functional groups as indicated by IR spectra and the hydration of the cement near the crumb rubber was enhanced as shown by SEM, leading to stronger mortars.     

Properties of some cement stabilised compressed earth blocks and mortars

Findings from an on-going investigation into the effects of soil properties and cement content on physical characteristics of compressed earth blocks and soil mortars are presented. A series of test blocks were fabricated using a range of composite soils, stabilised with 5% and 10% cement, and compacted with a manual press. Results for saturated compressive strength, drying shrinkage, wetting/drying durability, and water absorption testing are presented in the paper. In conjunction with the block tests, workability and compressive strength characteristics of suitable soil: cement and cement: lime: sand mortars were also studied. Mortar consistency was assessed using cone penetrometer and slump tests. Water retention properties of the mortars were also measured. For a given compactive effort, the strength, drying shrinkage, and durability characteristics of the compressed earth blocks improved with increasing cement and reducing clay content. Slump testing proved the most reliable means of assessing soil: cement mortar consistency. Both the flow table and cone penetrometer tests were found to be unsuitable. Water retention properties of soil: cement mortars appear well-suited to typical unit water absorption characteristics. Mortar strengths were closely related to cement and clay contents, but as expected were less than the average unit strengths.     

The use of superabsorbent polymers to reduce cracking of bonded mortar overlays

The use of superabsorbent polymers (SAP) was found to significantly improve cracking characteristics of normal strength bonded mortar overlays containing silica fume. Mortars were designed with two water/binder ratios and three different SAP contents and tested for relevant material properties such as tensile strength, tensile relaxation, elastic modulus and drying shrinkage. With respect to overlay cracking, SAP addition generally resulted in an improvement in all tested properties, especially with respect to increasing relaxation and reduced elastic modulus. To observe cracking in real bonded overlays, mortars were cast on a rigid substrate and their cracking behavior observed for a period of approximately 7 weeks. The results indicate that SAP additions of 0.4% and 0.6% are very effective in reducing cracking in bonded mortar overlays with water/binder ratios of 0.45 and 0.55, respectively.